The proposed research has as an objective the determination of the molecular structure of two mitochondrial dehydrogenases and a lipoprotein complex from amphibian oocytes. The studies on the mitochondrial dehydrogenases, L-3 hydroxyacyl coenzyme A dehydrogenase and malate dehydrogenase, involve single crystal X-ray analysis to near atomic resolution. The structure of a functionally related enzyme, the cytoplasmic form of malate dehydrogenase, has already been determined by similar methods. The long range objectives of the structural studies on the dehydrogenases is to compare in detail molecular models of these enzymes. Interpetation of the differences and similarities in the models will be done in terms of their different catalytic properties. A comparison of the molecular structure of the mitochondrial dehydrogenases with the known structure of the cytoplasmic enzymes should also provide insight as to their evolutionary relationships. Last of all these comparisons may be helpful in determining structural domains belonging to the mitochondrial enzymes which are responsible for their localization in mitochondria. The structural studies on the yolk lipoprotein complex from amphibian oocytes are a low resolution analysis approximately 25 Angstrom units using x-ray diffraction and electron microscopy. X-ray powder photographs have been used to determine the unit cell of the microcrystalline material. Electron microscope images of the negatively stained lattice will be improved by optical filtering experiments. The different filtered images of the lipoprotein molecule in projection will be correlated in an attempt to arrive at a suitable low resolution model. Experiments designed to locate the lipid binding regions in the model are also proposed.